1. Field of the Invention
The present invention relates to continuous rolling mills for rolling a strip (e.g., metal strip), and more specifically to a method of measuring strip crown in order to control both the strip thickness distribution (i.e., strip crown) in the strip lateral direction and the strip wave (i.e., flatness) of the strip longitudinal direction to desired values, respectively and a method of controlling the continuous rolling mills on the basis of the measuring method.
2. Description of the Prior Art
A hot finish rolling mill for controlling strip crown and flatness is disclosed by Hot rolling technology for improvement of dimensional accuracy! by Yasuyuki NISHIYAMA, on pages 81 to 90, Rolling Theory Committee Journal of Memorial Symposium of 100th Meeting of The Iron and Steel Institute of Japan, June 1994, for instance. In particular, on page 87, there are disclosed a crown and/or shape control system of a hot strip mill which composes of six stands, a profile gauge and a strip flatness sensor at the exit of the last stand. This system controls bendings on the bases of outputs of those sensors.
In this rolling mill, the work roll bendings are installed for only the last three stands, so that the rest are not feedback controlled. As a result, it is impossible to control both the strip crown and the flatness to desired values, respectively and satisfactorily. In addition, since nothing is explained of the practical operation of the work roll bendings, it is difficult to realize the control method in practice.
Further, the relationship among the virtual strip crown (referred to as mechanical strip crown, hereinafter) obtained when the rolling force distribution is uniform in the width direction of the rolled strip, the imprinting ratio, the inheritance coefficient from the entry strip crown to the delivery strip crown, etc. are explained in detail in Development in Shape and Crown Control Theory for Thin Sheet rolling! by Hiromi MATSUMOTO, on pages 155 to 176, Rolling Theory Committee Journal of Memorial Symposium of 30th Meeting of The Iron and Steel Institute of Japan, March 1985, for instance.
In this case, however, nothing is explained of the method of controlling the strip crown and the flatness to desired values, respectively, so that it is difficult to realize the control method in practice.